The present application claims priority to Japanese Applications Nos. P2000-110810 filed Apr. 12, 2000, and P2000-296189 filed Sep. 28, 2000, which applications are incorporated herein by reference to the extent permitted by law.
This invention relates to an optical recording medium, especially suitable for application to a phase change-versatile optical disc available for repetitive recording and erasure.
In recent data recording technologies, researches are being developed regarding optical recording systems. Optical recording systems can record and reproduce information signals without contacting a recording medium, and can attain higher recording densities as ten times or more as that those of magnetic recording systems. Additionally, optical recording systems have a number of advantages, including the availability for use with any type of memory such as reproduction-exclusive type, additional recording type and rewritable type. Thus, the optical recording systems are expected to be widely usable in industrial purposes and home-base purposes as a recording system that enables realization of inexpensive, large-capacity files.
Among those optical recording systems, optical magnetic discs and phase-versatile optical discs, for example, cope with rewritable memory modes.
Among them, a magneto-optical disc is configured such that its recording film made of a magnetic material is heated to or above a Curie point or a temperature compensation point to decrease the coercive force of the recording film, then an external recording magnetic field is applied to change the magnetic orientation of the recording film, and information signals are recorded, or magnetically read out. On the other hand, a phase change-versatile optical disc includes a recording film made of a phase change-versatile material in which a phase change between a crystalline state and an amorphous state reversibly occurs, and is configured such that its recording film is heated by irradiation of laser light, for example, to cause a change in phase in the recording film, thereby to record/erase information signals, or optically read out information signals.
As a conventional phase disc, CD-RW (compact disc-rewritable) is known and being spread. The format of CD-RW is shown below.
Medium
Recording bit length: 0.59 xcexcm per bit
Capacity: 640 MB (IS09660)
Track pitch: 1.6 xcexcm
Upon Recording
Wavelength (xcex) or irradiated laser light: xcex=780 nm
Numerical aperture of the optical system (NA): NA=0.50
Linear velocity: 1.2xcx9c4.8 m/s (equal velocity to four-times velocity)
Repeatable recording frequency: 1000 times or more
Upon Reproduction
Wavelength (xcex) or irradiated laser light: xcex=780 nm
Numerical aperture of the optical system (NA): NA=0.45
Reflectance: 15xcx9c25%
Modulation factor: 55xcx9c70%
Resolution: 45xcx9c60%
In order to realize such a phase optical disc under that regulation (specifically, CD-RW), AgInSbTe alloy series materials are used as phase materials, and Alxe2x80x94Ti alloys and Alxe2x80x94Cr alloys are used as materials of reflection films.
However, regarding such phase optical discs, further improvements in recording speed and reproducing speed are demanded, and at the same time, a larger recording capacity is desired. If an improvement of the linear velocity is tried toward realization of high-speed recording and high-speed reproduction among those requirements, the following problem will occur. That is, recording or reproduction of information signals at a higher linear velocity than the conventional maximum linear velocity (about 4.8 m/s (four-times velocity) in linear velocity) will invite a deterioration of jitters and decrease of the modulation factor. Therefore, practically acceptable recording characteristics could not be obtained.
Additionally, according to the knowledge of the Inventor, even if it is tried to reduce the track pitch or increase NA, for example, for the purpose of increasing the recording capacity than that of the conventional optical recording mediums, it is very difficult to obtain satisfactory recording/reproduction characteristics in the high linear velocity range. Therefore, it has been demanded to develop a technique capable of increasing the capacity while ensuring satisfactory recording/reproduction characteristics even in the high linear velocity range.
It is therefore an object of the invention to provide an optical recording medium that can ensure practically satisfactory recording characteristics even under the high linear velocity range and can be increased in recording capacity to realize a large-capacity recording medium.
According to the first aspect of the invention, there is provided an optical recording medium having a substrate defining a corrugated and uneven groove track configuration on one major surface thereof; and a first dielectric film, a phase recording film, a second dielectric film and a reflection film which are sequentially stacked on the major surface of the substrate, characterized in:
the phase recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AgPdCu alloy material;
in the GeInSbTe alloy material forming the phase recording film, content of Ge being in the range from 1 weight % to 8 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.2 times to 3.0 times, and in the AgPdCu alloy material forming the reflection film, content of Pd being in the range of 0.9 weight % to 1.5 weight %, and content of Cu being in the range of 0.9 weight % to 1.1 weight %,
depth of each depression in the groove track configuration being in the range from 35 nm to 44 nm,
distance between two adjacent boundaries at opposite sides of the depression among boundaries between crests and depressions being in the range of 0.35 xcexcm to 0.50 xcexcm,
thickness of the first dielectric film being in the range of 75 nm to 95 nm, thickness of the phase recording film being in the range of 12 nm to 20 nm, thickness of the second dielectric film being in the range of 16 nm to 28 nm, and thickness of the reflection film being in the range of 80 nm to 160 nm.
According to the second aspect of the invention, there is provided an optical recording medium having a substrate defining a corrugated and uneven groove track configuration on one major surface thereof; and a first dielectric film, a phase recording film, a second dielectric film and a reflection film which are sequentially stacked on the major surface of the substrate, characterized in:
the phase recording film being made of a GeInSbTe alloy material, and the reflection film being made of an AlCu alloy material;
in the GeInSbTe alloy material forming the phase recording film, content of Ge being in the range from 1 weight % to 8 weight %, content of In being in the range from 2 weight % to 6 weight %, and ratio of Sb relative to Te being in the range of 2.2 times to 3.0 times, and in the AlCu alloy material forming the reflection film, content of Cu being not larger than 1.5 weight %,
depth of each depression in the groove track configuration being in the range from 35 nm to 44 nm,
distance between two adjacent boundaries at opposite sides of the depression among boundaries between crests and depressions being in the range of 0.35 xcexcm to 0.50 xcexcm,
thickness of the first dielectric film being in the range of 75 nm to 95 nm, thickness of the phase recording film being in the range of 12 nm to 20 nm, thickness of the second dielectric film being in the range of 16 nm to 28 nm, and thickness of the reflection film being in the range of 80 nm to 160 nm.
In the present invention, width of the interval between two adjacent boundaries interposing a recess therebetween is preferably in the range from 0.40 xcexcm to 0.50 xcexcm.
In the present invention, ratio of Sb relative to Te is preferably in the range from 2.2 times to 2.8 times.
In the present invention, the optical recording medium is typically available for recording and/or erasing information signals by irradiating at least the phase recording film with light having a wavelength in the range from 775 nm to 795 nm, more specifically around 780 nm.
In the present invention, numerical aperture of the lens in the optical system used upon recording and/or erasing information signals on or from the optical recording medium is typically in the range from 0.54 to 0.56, and more specifically, approximately 0.55.
In the present invention, the recording linear density in the optical recording medium is typically about 0.44 xcexcm per bit.
In the present invention, the first dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction to the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 (kxe2x89xa60.3) is used as the material of the first dielectric film.
In the present invention, the second dielectric film is made of a material with a low absorptance to laser light of the optical system used upon recording/reproduction of the optical recording medium. Preferably, a material having a value of extinction coefficient k not higher than 0.3 (kxe2x89xa60.3) is used as the material of the first dielectric film.
In the present invention, the optical recording medium is a rewritable optical recording medium using a phase material as the recording film. Additionally, the track pitch in the uneven groove track configuration in the optical recording medium according to the invention is about 1.1 xcexcm, for example. The optical recording medium according to the invention may be CD-RW (compact disc-rewritable) having a recording capacity around 1.3 GB.
According to the optical recording medium having the above-summarized configuration according to the invention, the phase recording film in the optical recording medium is made of a GeInSbTe alloy material; the reflection film is made of an AgPdCu alloy material or AlCu alloy material; the GeInSbTe alloy material forming the phase recording film contains Ge in the range from 1 weight % to 8 weight %, In in the range from 2 weight % to 6 weight %, and Sb in the range from 2.2 times to 3.0 times of Te; the reflection film, when made of an AgPdCu alloy material, contains Pd in the range from 0.9 weight % to 1.5 weight % and Cu in the range from 0.9 weight % to 1.1 weight %; the reflection film, when made of an AlCu alloy material, contains Cu by 1.5 weight %; depth of each recess in the uneven groove track configuration along the major surface of the substrate is in the range from 35 nm to 45 nm; distance between two boundaries, among boundaries between lands and grooves of the groove tracks, is in the range from 0.35 xcexcm to 0.50 xcexcm; thickness of the first dielectric film is in the range from 75 nm to 95 nm; thickness of the phase recording film is in the range from 12 nm to 20 nm; thickness of the second dielectric film is in the range from 16 nm to 28 nm, and thickness of the reflection film is in the range from 80 nm to 160 nm. This configuration can prevent deterioration of jitters and a decrease of the modulation factor even when the linear velocity is increased upon recording and/or erasing information signals, and thereby ensures satisfactory recording characteristics in the optical recording medium.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.